Units producing carbon monoxide and hydrogen can be divided into two parts:                syngas generation (mixture containing H2, CO, CH4, CO2, Ar, H2O and N2 essentially).        syngas purification. This comprises:        a liquid solvent scrubbing unit to remove most of the sour gases contained in the syngas        an adsorbent bed purification unit        a cryogenic separation unit called cold box for producing CO.        
In general, fuel is consumed in order to preheat the feed, and to superheat the steam, which may be consumed by the process and/or exported.
The quantity of fuel required is generally defined by the needs of the syngas generating unit.
Since the fuel consists of the waste gases from the separation unit (such as cold box CO, H2 PSA, membranes, etc.), it is generally desirable to have an external fuel make-up to ensure the control of the fuel balance imposed by the process.
In the case in which the quantity of waste gases exceeds the fuel needs of the plant, the surplus can be burned in a boiler to produce steam, or can be exported. In the case of steam production, this generally incurs the investment of a dedicated boiler.